1. Field of the Invention
The present invention relates to metallic seals for fluid flow control valves.
2. Description of the Prior Art
Flow control valves, such as servocontrolled valves for mass flow controllers, have movable valve heads which commonly carry an elastomeric disc or seal. The valve head moves relative to an end surface of a valve body that has an orifice in it, to control flow through the orifice and to seat on the valve body to completely stop flow. Elastomeric or plastic seal materials are limited in application because of incompatibility of the seal material with the fluid medium. In some instances solid metal discs have been used for valve heads, which solves the compatibility problem but does not allow complete shut-off unless very large forces are used for seating the valve head.